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Exchanges of identity in deep space

A new study published in Physical Review Letters

Like in a nail-biting thriller full of escapes and subterfuge, photons from far-off light sources, such as blazars, could go up against a continuous exchange of identity in their journey through the Universe. This is an operation that would allow these very tiny particles of light to escape an enemy which, if encountered, would annihilate them. This is the phenomenon studied by a group of researchers from the University of Salento, Bari, the National Institute for Nuclear Physics (INFN), the National Institute for Astrophysics (INAF) and SISSA thanks to brand new simulation models that reproduce the complexity of the cosmos as never before. Normally, very high energy photons (gamma rays) should "collide" with the background light emitted by galaxies transformed into pairs of matter and antimatter particles, as envisaged by the Theory of Relativity. For this reason, the sources of very high energy gamma rays should appear significantly less bright than what is observed in many cases. A possible explanation for this surprising anomaly is that light photons are transformed into hypothetical weakly-interacting particles, "axions" which, in turn, would change into photons, all due to the interaction with magnetic fields. With these metamorphoses, a part of the photons would escape interaction with the intergalactic background light that would make them disappear. The importance of this process is emphasised by the study published on Physical Review Letters, which re-created an extremely refined model of the Cosmic Web, a network of filaments composed of gas and dark matter present throughout the Universe and of its magnetic fields. The aforementioned effects are now awaiting comparison with those obtained experimentally through Cherenkov Telescope Array new generation telescopes.